Environmental Engineering Reference
In-Depth Information
Permanent damage
begins after 8-hour
exposure
Noise Levels (in dbA)
85
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
Boom
cars
Normal
breathing
Whisper
Quiet
rural area
Rainfall
Vacuum
cleaner
Lawn
mower
Rock music
Earphones
at loud level
Air raid
siren
Quiet
room
Normal
conversation
Average
factory
Chain
saw
Thunderclap
(nearby)
Military
rifle
Figure 7-19
Noise levels
(in decibel-A [dbA] sound pressure units) of some common sounds. You are being ex-
posed to a sound level high enough to cause permanent hearing damage if you need to raise your voice to be
heard above the racket, if a noise causes your ears to ring, or if nearby speech seems muffled. Prolonged exposure
to lower noise levels and occasional loud sounds may not damage your hearing but can greatly increase internal
stress. Noise pollution can be reduced by modifying noisy activities and devices, shielding noisy devices or
processes, shielding workers or other receivers from the noise, moving noisy operations or things away from peo-
ple, and using antinoise (a technology that cancels out one noise with another).
(especially if adequate drinking water and sewage sys-
tems are not available), physical injuries (mostly from
industrial and traffic accidents), and excessive noise
(Figure 7-19).
Cities generally are warmer, rainier, foggier, and
cloudier than suburbs and nearby rural areas. The
enormous amounts of heat generated by cars, facto-
ries, furnaces, lights, air conditioners, and heat-
absorbing dark roofs and roads in cities create an
urban
heat island
that is surrounded by cooler suburban and
rural areas. As cities grow and merge (Figure 7-14),
their heat islands may merge and keep polluted air
from being diluted and cleansed.
The artificial light created by cities also hinders as-
tronomers from conducting their research and affects
various plant and animal species. Species vulnerable
to
light pollution
include endangered sea turtles that
lay their eggs on beaches at night and migrating birds
that are lured off course by the lights of high-rise
buildings and fatally collide with them.
Urban areas can intensify poverty and social prob-
lems. Crime rates also tend to be higher in these areas
than in rural areas (Connections, right). And, of
course, urban areas are more likely and desirable tar-
gets for terrorist acts.
Economics Case Study: The Urban Poor
in Developing Countries
Most of the urban poor in developing countries live in
crowded, unhealthy, and dangerous conditions, but
many are better off than the rural poor.
Many of the world's poor live in
squatter settlements
and s
hantytowns
on the outskirts of most cities in de-
veloping countries (Figure 7-20), some perched precar-
Figure 7-20
Global outlook:
extreme poverty forces hundreds
of millions of people to live in slums such as this one in Rio de
Janeiro, Brazil, where adequate water supplies, sewage dis-
posal, and other services don't exist.
